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排序方式: 共有421条查询结果,搜索用时 46 毫秒
171.
172.
An encapsulation system designed to give long-lasting effectiveness of the insect growth regulator (IGR) cyromazine (Neporex) against Culex pipiens (Culicidae) mosquito larvae was developed. The main thrust of the research was to develop a simple method for preparing controlled-release formulations by means of an extrusion technique in combination with a supplementary coating and to study the release characteristics and effectiveness of the formulations. A series of formulations were prepared with low-density polyethylene (LDPE 600) for the matrix and with polyurea or one of four types of polyurethane for the coating. The rate of release of the active material from the controlled-release formulations was determined in an in vitro dissolution system. The biological activity of the controlled-release formulations was tested in vivo against C. pipiens larvae. 相似文献
173.
Inducible defenses are dynamic traits that modulate the strength of both plant-herbivore and herbivore-carnivore interactions. Surprisingly few studies have considered the relative contributions of induced plant and herbivore defenses to the overall balance of bottom-up and top-down control. Here we compare trophic cascade strengths using replicated two-level and three-level plankton communities in which we systematically varied the presence or absence of induced defenses at the plant and/or herbivore levels. Our results show that a trophic cascade, i.e., significantly higher plant biomass in three-level than in two-level food chains, occurred whenever herbivores were undefended against carnivores. Trophic cascades did not occur when herbivores exhibited an induced defense. This pattern was obtained irrespective of the presence or absence of induced defenses at the plant level. We thus found that herbivore defenses, not plant defenses, had an overriding effect on cascade strength. We discuss these results in relation to variation in cascade strengths in natural communities. 相似文献
174.
Schaffner U Ridenour WM Wolf VC Bassett T Müller C Müller-Schärer H Sutherland S Lortie CJ Callaway RM 《Ecology》2011,92(4):829-835
One commonly accepted mechanism for biological invasions is that species, after introduction to a new region, leave behind their natural enemies and therefore increase in distribution and abundance. However, which enemies are escaped remains unclear. Escape from specialist invertebrate herbivores has been examined in detail, but despite the profound effects of generalist herbivores in natural communities their potential to control invasive species is poorly understood. We carried out parallel laboratory feeding bioassays with generalist invertebrate herbivores from the native (Europe) and from the introduced (North America) range using native and nonnative tetraploid populations of the invasive spotted knapweed, Centaurea stoebe. We found that the growth of North American generalist herbivores was far lower when feeding on C. stoebe than the growth of European generalists. In contrast, North American and European generalists grew equally well on European and North American tetraploid C. stoebe plants, lending no support for an evolutionary change in resistance of North American tetraploid C. stoebe populations against generalist herbivores. These results suggest that biogeographical differences in the response of generalist herbivores to novel plant species have the potential to affect plant invasions. 相似文献
175.
176.
One can say very little about the relative merits of temporary versus permanent salt marsh mosquito control from the Carlson and DeBord study (J. Environ. Econ. Manag. 3, 142–153 (1976)). Their conclusion that temporary control is more cost effective than permanent control is suspect because of their interpretation and use of the data which entered their analyses and because of their interpretation of analytical results. 相似文献
177.
178.
Stephan Baumgartner Martin Wolf Peter Skrabal Felix Bangerter Peter Heusser André Thurneysen Ursula Wolf 《Die Naturwissenschaften》2009,96(9):1079-1089
Quantitative meta-analyses of randomized clinical trials investigating the specific therapeutic efficacy of homeopathic remedies
yielded statistically significant differences compared to placebo. Since the remedies used contained mostly only very low
concentrations of pharmacologically active compounds, these effects cannot be accounted for within the framework of current
pharmacology. Theories to explain clinical effects of homeopathic remedies are partially based upon changes in diluent structure.
To investigate the latter, we measured for the first time high-field (600/500 MHz) 1H T1 and T2 nuclear magnetic resonance relaxation times of H2O in homeopathic preparations with concurrent contamination control by inductively coupled plasma mass spectrometry (ICP-MS).
Homeopathic preparations of quartz (10c–30c, n = 21, corresponding to iterative dilutions of 100−10–100−30), sulfur (13x–30x, n = 18, 10−13–10−30), and copper sulfate (11c–30c, n = 20, 100−11–100−30) were compared to n = 10 independent controls each (analogously agitated dilution medium) in randomized and blinded experiments. In none of the
samples, the concentration of any element analyzed by ICP-MS exceeded 10 ppb. In the first measurement series (600 MHz), there
was a significant increase in T1 for all samples as a function of time, and there were no significant differences between homeopathic potencies and controls.
In the second measurement series (500 MHz) 1 year after preparation, we observed statistically significant increased T1 relaxation times for homeopathic sulfur preparations compared to controls. Fifteen out of 18 correlations between sample
triplicates were higher for controls than for homeopathic preparations. No conclusive explanation for these phenomena can
be given at present. Possible hypotheses involve differential leaching from the measurement vessel walls or a change in water
molecule dynamics, i.e., in rotational correlation time and/or diffusion. Homeopathic preparations thus may exhibit specific
physicochemical properties that need to be determined in detail in future investigations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
179.
180.
Max A. Moritz Tadashi J. Moody Lori J. Miles Matthew M. Smith Perry de Valpine 《Environmental and Ecological Statistics》2009,16(2):271-289
Statistical characterization of past fire regimes is important for both the ecology and management of fire-prone ecosystems.
Survival analysis—or fire frequency analysis as it is often called in the fire literature—has increasingly been used over
the last few decades to examine fire interval distributions. These distributions can be generated from a variety of sources
(e.g., tree rings and stand age patterns), and analysis typically involves fitting the Weibull model. Given the widespread
use of fire frequency analysis and the increasing availability of mapped fire history data, our goal has been to review and
to examine some of the issues faced in applying these methods in a spatially explicit context. In particular, through a case
study on the massive Cedar Fire in 2003 in southern California, we examine sensitivities of parameter estimates to the spatial
resolution of sampling, point- and area-based methods for assigning sample values, current age surfaces versus historical
intervals in generating distributions, and the inclusion of censored (i.e., incomplete) observations. Weibull parameter estimates
were found to be roughly consistent with previous fire frequency analyses for shrublands (i.e., median age at burning of ~30–50 years
and relatively low age dependency). Results indicate, however, that the inclusion or omission of censored observations can
have a substantial effect on parameter estimates, far more than other decisions about specifics of sampling.
相似文献
Max A. MoritzEmail: |